Dont use let .. in when multiline after "in"or formatting from AST. S…

…hould fix #384 (#393)

dont use let .. in when formatting from AST

src/Fantomas.Tests/FormatAstTests.fs

@@ -4,13 +4,23 @@ open NUnit.Framework
 open FsUnit
 open Fantomas.Tests.TestHelper
 
-[<Test>]
-let ``Format the ast works correctly with no source code``() =
+let formatAst code =
     let inputExp =
-        "()" |> Input
+        code |> Input
         |> toSynExprs
         |> List.head
 
     fromSynExpr inputExp
     |> function Input x -> x.TrimEnd('\r', '\n')
-    |> should equal "()"
+    |> fun s -> s.Replace("\r\n", "\n")
+
+[<Test>]
+let ``Format the ast works correctly with no source code``() =
+    formatAst "()"
+    |> should equal "()"
+
+[<Test>]
+let ``let in should not be used``() =
+    formatAst "let x = 1 in ()"
+    |> should equal """let x = 1
+()"""

src/Fantomas.Tests/LetBindingTests.fs

@@ -30,4 +30,52 @@ let f () =
     let x = 1   // the "in" keyword is available in F#
     let y = 2
     x + y
+"""
+
+[<Test>]
+let ``multiple let in lines, should remove in, block comment`` () =
+    let codeSnippet = """
+let f () = 
+  let x = 1 in   (* the "in" keyword is available in F# *)
+    let y = 2 in 
+      x + y
+"""
+
+    formatSourceString false codeSnippet config
+    |> should equal """let f() =
+    let x = 1   (* the "in" keyword is available in F# *)
+    let y = 2
+    x + y
+"""
+
+[<Test>]
+let ``multiline let in, should remove in`` () =
+    let codeSnippet = """
+let f () =
+  let x = 1 in if true 
+               then x
+               else x
+"""
+
+    formatSourceString false codeSnippet config
+    |> should equal """let f() =
+    let x = 1
+    if true then x
+    else x
+"""
+
+[<Test>]
+let ``multiline let in, should remove in 2`` () =
+    let codeSnippet = """
+let f () =
+  let x = 1 in (while true do ()
+                x)
+"""
+
+    formatSourceString false codeSnippet config
+    |> should equal """let f() =
+    let x = 1
+    (while true do
+         ()
+     x)
 """

src/Fantomas/CodePrinter.fs

@@ -658,11 +658,13 @@ and genExpr astContext synExpr =
 
     | TypeApp(e, ts) -> genExpr astContext e -- "<" +> col sepComma ts (genType astContext false) -- ">"
     | LetOrUses(bs, e) ->
-        let isInSameLine =
+        let isFromAst (ctx: Context) = ctx.Content = String.Empty
+        let isInSameLine ctx =
             match bs with
-            | [_, LetBinding(ats, px, ao, isInline, isMutable, p, _)] -> p.Range.EndLine = e.Range.StartLine
+            | [_, LetBinding(ats, px, ao, isInline, isMutable, p, _)] -> 
+                not (isFromAst ctx) && p.Range.EndLine = e.Range.StartLine && not(checkBreakForExpr e)
             | _ -> false
-        atCurrentColumn (genLetOrUseList astContext bs +> ifElse isInSameLine (!- " in ") sepNln +> genExpr astContext e)
+        atCurrentColumn (genLetOrUseList astContext bs +> ifElseCtx isInSameLine (!- " in ") sepNln +> genExpr astContext e)
 
     // Could customize a bit if e is single line
     | TryWith(e, cs) -> 

src/Fantomas/Context.fs

@@ -202,6 +202,9 @@ let internal optPre (f2 : _ -> Context) (f1 : Context -> _) o f (ctx : Context)
 let internal ifElse b (f1 : Context -> Context) f2 (ctx : Context) =
     if b then f1 ctx else f2 ctx
 
+let internal ifElseCtx cond (f1 : Context -> Context) f2 (ctx : Context) =
+    if cond ctx then f1 ctx else f2 ctx
+
 /// Repeat application of a function n times
 let internal rep n (f : Context -> Context) (ctx : Context) =
     [1..n] |> List.fold (fun c _ -> f c) ctx

src/Fantomas/TokenMatcher.fs

@@ -694,8 +694,10 @@ let integrateComments (config:Fantomas.FormatConfig.FormatConfig) compilationDef
         | (Marked(inToken,_,_)::oldTokens),  (NewLine newTokText :: moreNewTokens) ->
             Debug.WriteLine(sprintf "emitting newline in new tokens '%s'" newTokText)
             let nextOldTokens =
-                match (inToken) with 
-                | Tok(fsInToken,_) when (fsInToken.TokenName = "IN") ->
+                match (inToken, oldTokens) with 
+                | Tok(fsInToken,_), (WhiteSpaceTokens (_, LineCommentToken false _ :: _))
+                | Tok(fsInToken,_), (WhiteSpaceTokens (_, BlockCommentToken _ :: _))
+                    when (fsInToken.TokenName = "IN") ->
                     // find tokens before newline in old source
                     let tokensBeforeNewline =
                         oldTokens